Ferrofluid cap seal for spindle motor

ABSTRACT

A hard disk drive spindle motor has a hub, a drive shaft, and a bearing therebetween. The spindle motor also has a ferrofluid seal to prevent any incidental oil emissions from the bearing from entering the drive. A ferrofluid cap is mounted on the axial end of the spindle motor for sealing the ferrofluid seal. The cap is a flat ring and has an elastomeric pad around its outer edge. The pad seats in a recess in the bore of the hub. The cap does not touch the shaft as it rotates with the hub about the shaft. Any excess ferrofluid from the ferrofluid seal is forced radially outward away from the shaft by centrifugal force. The cap contains the excess ferrofluid within the spindle motor and prevents it from entering other areas of the disk drive.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field

[0002] This invention relates in general to sealing motors and inparticular to a ferrofluid cap seal for a hard disk drive spindle motor.

[0003] 2. Background Art

[0004] Referring to FIG. 1, a schematic drawing of an informationstorage system comprising a magnetic hard disk drive 11 is shown. Drive11 has a base 13 containing a plurality of stacked, parallel magneticdisks 15 (one shown) which are closely spaced apart. Disks 15 arerotated by a spindle motor (not shown) located therebelow about acentral drive hub 17. An actuator 21 is pivotally mounted to base 13about a pivot assembly 23. A controller 19 is mounted to base 13 forselectively moving actuator 21 as will be described below.

[0005] Actuator 21 has a mounting support 25, a pair of parallel,cantilevered load beams or suspensions 27 extending from mountingsupport 25, and a head gimbal assembly 29 having at least one magneticread/write head secured to each suspension 27 for magnetically readingdata from or magnetically writing data to disks 15. Suspensions 27 havea spring-like quality which biases or maintains them in parallelrelationship relative to one another. A motor assembly 31 having aconventional voice coil motor is also mounted to pivot assembly 23opposite head gimbal assemblies 29. Movement of actuator 21 (indicatedby arrows) moves head gimbal assemblies 29 radially across tracks on thedisks 15 until the heads on assemblies 29 settle on the target tracks.

[0006] The spindle motor contains bearings that incidentally emit verysmall amounts of oil vapor and aerosol droplets of grease. These arepotential sources of contamination in the disk drive. Some prior artdisk drive use ferrofluid seals to seal the bearings. Ferrofluid sealsare practically impermeable to emissions from bearings and function bysuspending magnetically attracted fluid across an opening. The suspendedfluid, which is essentially frictionless, forms an effective liquidseal.

[0007] Some prior art ferrofluid seals allow a very small amount offerrofluid to migrate into the disk drive over time. In addition, aferrofluid droplet may be inadvertantly dispensed onto the top of theseal assembly, or excess ferrofluid may be dispensed into the seal. Suchleakage and excess can cause contamination of the drive leading to dataloss or even catastrophic failure of the drive. In the prior art,ferrofluid caps have been used to seal ferrofluid seals. Techniques forsecuring the caps in the spindle motor have included adhesive bondingand mechanical snap fits. The mechanical snap fit, annular caps wereprovided with slits and a lip around their outer perimeter to enablethem to be snapped over the backiron of the spindle motor. The snap fitcaps were designed to protect the ferrofluid seal while handling duringmanufacturing. Unfortunately, the bonding and the subsequent inspectionprocess are expensive, and the snap fit cap designs provide noprotection against ferrofluid escape. Thus, an improved cap forpreventing the escape of ferrofluid from ferrofluid seals is needed.

SUMMARY OF THE INVENTION

[0008] A hard disk drive spindle motor has a hub, a drive shaft, and abearing therebetween. The spindle motor also has a ferrofluid seal toprevent any incidental oil emissions from the bearing from entering thedrive. A ferrofluid cap is mounted on the axial end of the spindle motorfor sealing the ferrofluid seal. The cap is a flat ring and has anelastomeric pad around its outer edge. The pad seats in a recess in thebore of the hub. The cap does not touch the shaft as it rotates with thehub about the shaft. Any excess ferrofluid from the ferrofluid seal isforced radially outward away from the shaft by centrifugal force. Thecap contains the excess ferrofluid within the spindle motor and preventsit from entering other areas of the disk drive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the features, advantages and objectsof the invention, as well as others which will become apparent, areattained and can be understood in more detail, more particulardescription of the invention briefly summarized above may be had byreference to the embodiment thereof which is illustrated in the appendeddrawings, which drawings form a part of this specification. It is to benoted, however, that the drawings illustrate only a preferred embodimentof the invention and is therefore not to be considered limiting of itsscope as the invention may admit to other equally effective embodiments.

[0010]FIG. 1 is a schematic plan view of a hard disk drive.

[0011]FIG. 2 is a schematic sectional side view of a disk drive spindlemotor that is constructed in accordance with the invention.

[0012]FIG. 3 is an enlarged schematic sectional side view of a portionof the spindle motor of FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] Referring to FIG. 2, a hard disk drive spindle motor 41 having anouter housing or hub 43 with an axis 45 and a concentric drive shaft 47is shown. In the embodiment shown, shaft 47 stationarily mounts to thedisk drive base (not shown) and hub 43 is rotatable relative thereto.Alternatively, hub 43 may be mounted to the base and shaft 47 couldrotate relative to it. At least one rotary bearing 49 (two shown) ismounted between hub 43 and shaft 47 to enhance the stability of hub 43as it rotates. During operation, bearing 49 incidentally emits smallamounts oil vapor and aerosol droplets of grease which are a potentialsource of contamination in the disk drive.

[0014] Spindle motor 41 contains a ferrofluid seal 51 to seal bearing 49in the drive. Ferrofluid seal 51 is located axially outside or outboardof bearing 49, and is practically impermeable to emissions from bearing49. The ferrofluid in seal 51 contains very small magnetic particleswhich are suspended in a carrier fluid. Ferrofluid seal 51 functions bysuspending the magnetically attracted fluid between hub 43 and shaft 47to complete the magnetic circuit. The suspended fluid, which isessentially frictionless, forms an effective liquid seal between therotating hub 43 and shaft 47.

[0015] Referring now to FIGS. 2 and 3, spindle motor 51 also has aferrofluid cap 61. Cap 61 is located on one axial end of motor 51, onthe axially outboard side of ferrofluid seal 51, opposite of bearing 49.Cap 61 comprises a substantially flat, solid disc 63 without slits orholes except for a central hole 65. Disc 63 may be configured for avariety of applications, but is preferably formed from stamped stainlesssteel or like materials. Central hole 65 accommodates the end of shaft47 and is free of contact therewith. An annular pad 67 is integrallymounted to the outer edge or circumference 69 of disc 63. In thepreferred embodiment, pad 67 is formed from an elastomer or equivalentconforming material and is molded to circumference 69. Pad 67 is closelyreceived in an annular concave recess 71 in the bore 73 of hub 43. Withpad 67, cap 61 forms an additional seal in hub 43 that does not requireadhesive.

[0016] In operation, cap 61 is pressed or installed in spindle motor 61such that pad 69 forms a tight elastomeric or equivalent conformingmaterial seal in recess 71. Cap 61 is free of contact with shaft 47 androtates with hub 43 about the stationary shaft 47. Any excess ferrofluidor ferrofluid migration from the dynamic ferrofluid seal 51 is directedradially outward away from shaft 47 by way of centrifugal force. As aresult, cap 61 forms an effective seal around bore 73 that contains anyexcess ferrofluid within spindle motor 41 and prevents it from enteringother areas of the disk drive.

[0017] The invention has several advantages. The ferrofluid cap relieson a press-fit elastomeric seal around its circumferential edge toprevent ferrofluid from entering the disk drive. The cap does not useadhesives or mechanical snap features to achieve the seal. This cap isrelatively inexpensive compared to prior art solutions and providessuperior sealing capability.

[0018] While the invention has been shown or described in only some ofits forms, it should be apparent to those skilled in the art that it isnot so limited, but is susceptible to various changes without departingfrom the scope of the invention.

We claim:
 1. An apparatus, comprising: a hub having a central axis, abore, an annular recess formed in the bore, and an axial end; a shaftmounted in the hub concentric with the axis, the hub and shaft beingrotatable relative to each other; a bearing mounted between the shaftand the hub; a ferrofluid seal mounted axially outboard of the bearingbetween the shaft and the hub for sealing the bearing in the hub, theferrofluid seal containing ferrofluid; a solid ferrofluid cap forsealing the ferrofluid in the hub, the cap having an outer edge mountedin the recess in the bore of the hub axially outboard of the ferrofluidseal, and an axial hole through which the shaft extends, the cap beingfree of contact with the shaft.
 2. The apparatus of claim 1 , furthercomprising an elastomeric seal mounted to the outer edge of theferrofluid cap for engaging the annular recess in the bore of the hub toform a seal.
 3. The apparatus of claim 1 wherein the ferrofluid cap is acircular disc, and the outer edge and axial hole of the cap arecircular.
 4. The apparatus of claim 1 wherein the elastomeric seal ismolded to the cap.
 5. The apparatus of claim 1 wherein the ferrofluidcap is free of adhesive bonds with respect to the hub.
 6. The apparatusof claim 1 wherein the bore of the hub has an annular concave recess forengaging the outer edge of the cap.
 7. A rotational apparatus for a harddisk drive, comprising: a hub having a central axis, a bore, an annularrecess formed in the bore, and an axial end; a shaft mounted in the hubconcentric with the axis, the hub and the shaft being rotatable relativeto each, other; a bearing mounted between the shaft and the hub; aferrofluid seal mounted axially outboard of the bearing between theshaft and the hub for sealing the bearing in the hub, the ferrofluidseal containing ferrofluid; a solid ferrofluid cap mounted in theannular recess in the bore of the hub axially outboard of the ferrofluidseal for sealing the ferrofluid in the hub, the cap comprising acircular disc with an outer circumferential edge and an axial hole thatis free of contact with the shaft; and an elastomeric seal mounted tothe outer circumferential edge of the ferrofluid cap for engaging theannular recess in the bore of the hub to form a seal.
 8. The rotationalapparatus of claim 7 wherein the elastomeric seal is molded to the cap.9. The rotational apparatus of claim 7 wherein the cap is free ofadhesive bonds with respect to the hub.
 10. The rotational apparatus ofclaim 7 wherein the bore of the hub has an annular recess for engagingthe cap.
 11. A rotational apparatus for a hard disk drive, comprising: ahub having a central axis, a bore with an annular concave recess, and anaxial end; a shaft rotatably mounted in the hub concentric with theaxis; a bearing mounted between the shaft and the hub; a ferrofluid sealmounted axially outboard of the bearing between the shaft and the hubfor sealing the bearing in the hub, the ferrofluid seal containingferrofluid; a ferrofluid cap mounted in the annular concave recess inthe bore of the hub axially outboard of the ferrofluid seal for sealingthe ferrofluid in the hub, the cap comprising a solid circular disc withan outer circumferential edge and an axial hole for remaining free ofcontact with the shaft; an elastomeric seal integrally formed on theouter circumferential edge of the cap for engaging the annular concaverecess in the bore of the hub to form a seal; and wherein theelastomeric seal is free of adhesive bonds with respect to the hub.